Contact-free high frequency commutator



July 5, 1960 CARL--ERIK GRANQVIST 2,944,230

CONTACT-FREE HIGH FREQUENCY COMMUTATOR Filed June 24, 1957 ATTORNEYJJ retested July 5, 1950 Free CONTACT-FREE HIGH FREQUENCY COMMUTATOR When commutating high frequencies for radio purposes, especially ultra high frequencies, known switches with contacts cause many problems due to variation of the contact resistance which causes noise, losses of power and so on. For this reason, as a rule, capacitive commutators were used, but these have the disadvantage.

that they give, due to their interior capacity, a very small band-width. When a greater band width was desired, with the high frequency commutators hitherto known, it was necessary to use movable contacts, primarily slide contacts.

. The present invention refers to a contact-free commutator for high frequency current, which will give a wide band-width satisfactory for all practical purposes. The invention will be further described with reference to the attached drawing, in which Fig. 1 is a schematical diagram for explanation of the principle forming the basis of the present invention, in a simplified form, and Fig. 2 shows a corresponding diagram for a somewhat more complicated case, whereas Figs, 38 show six different forms of execution of the invention.

The principle forming the basis of the present invention shall now be described with reference to Fig. 1. In this figure 10 is the end of an input line conductor, and 11 is the beginning of an output line conductor. The two conductors run in parallel a distance forming M4 of the wave length of the transferred alternating current. By means of the bent end parts 12, 13, both of the line conductors 10 and 11 are metallically connected to a tap or the like 14 acting as ground, which may for instance be formed by a piping of some electrically well conducting metal. The coupling factor between the two line conductors 10 and 11, regarding their dimensions and mutual distances, is indicated by k. This can easily be brought to accept values in the order of magnitude up to 0.8. Further the characteristics of the two lines are indicated'by Z the characteristic, of course, is the same for both of said lines. The output lineis also assumed to be ended with a load Z for adaption. Fnally it is assumed for generalizing the shown case, that the common line length, which should in the special case be M4, forms the electrical radian measure with respect to the frequency of the power transferred.

Under these conditions, one will according to known laws obtain the following relation between input characteristic Z measured in the direction onto the load, and the line characteristic Z If now 45 should be equal to 1r/2 or with other words 90, then cos will be equal to zero, and for values of 4:, which differ only unessentially from 90, one can with an allowable approximation in the above formula disregard the influence of cos 1 The formula will then be:

If this formula is solved with regard to k for 2 :2 then one will obtain k=0.7. Inserting thereafter k=0.7 in the formula and investigating the variation of the relation 2 /2 for different values of A, one will find, that this magnitude will only vary rather unessentially with A, and that one can regard the commutator as fully usable for frequencies up to about 33% above or below the frequency, respectively, at which the common line conductor length agrees with M4.

If for instance the commutator is tuned in this respect for a frequency of 300 megacycles, then it will be fully usable for a band of 200-400 megacycles.

However, one can also influence the band width of the commutator by choosing the relation Z /Z l.

It is now obvious that one can connect two such arrangements in series as indicated in Fig. 1. One then will get the arrangement shown in Fig. 2. In this arrangement, the input conductor is indicated 15 and the output conductor 16, whereas a coupling line conductor 17 is provided to take care of the coupling between the conductors 15 and 16. The coupling line conductor 17- thus is arranged in a way relative to the two conductors 15 and 16, that it extends in parallel to each of said conductors along substantiallly,)\/4 of its length, and if the two conductors 15 and 16, as shown in the drawing figure, are connected to the grounded tube 14 in substantially the same place, then the length of the coupling conductor 17 will consequently be M2. It is now obvious, that the same variation range for the frequency will be present in the arrangement according to Fig.- 2 as in the arrangement according to Fig. 1. It is also obvious, that if the coupling between the input line conductor 15 and the coupling conductor 17 and/or the coupling conductor 17 and the output line conductor 16 is changed, then the voltage transfer will also be changed in a corresponding way. The present invention is based upon the knowledge of these circumstances.

According to the invention the contact-free commutator for high frequency currents is composed of at least one input line conductor and at least one output line conductor, each of a length equal to one quarter of a wave-length of an electric oscillation within the transfer range and over all this length covered by a coupling conductor, which is common for the line conductors, and which is of the composite length of the parts of the line conductors contained in the commutator, and arrangements are further provided for varying the coupling degree between the coupling conductor, on one side, and each of the two line conductors, on the other side.

A very simple form of execution of this invention is shown in Fig. 3. Here one will find the grounded tube 14, which is in this case on its inner side provided with a flange 18. The two line conductors 15 and '16 are connected with the flange 18, for instance by being screwed into it in an axial direction. The pipe 14 is rigidly arranged, but inside the tube 14 a metallical cylinder 19 is arranged turnable about a shaft 20. This metallical cylinder 19 carries the coupling conductor 17. The line conductors 15 and 16 are in other respects equally arranged relative to the coupling conductor 18 as in Fig. 2. One will immediately understand, that a maximum coupling effect will be present between the line conduc tors 15 and 16', on the one side, and the coupling conductor 17, .onthe other side, when theseconductorsare the outer cylinder -32. of too thin a material.

in the positions indicated in Fig. 3, and that simultaneously the coupling is a minimum between line conductors and 16" which are displaced from the first conductors by 1,802. because. the coupling conductor .17 will. so to speak be fully shadowed from the field of the line cons ductors 15", 16" by the metallical cylinder 19. Between the ewo end positions, displaced by 180, thus a variable coupling can be provided, practically independent of the frequency of the transferred oscillation, as long as this is only in the same order of magnitude as the one for which this-commutator is tuned;

Figs. 4 and.5 show together a practical form of execution. of .a commutator described in connection .with vPig. 3. 'However, no separate line conductors have been arranged within the cylindrical cap and connected to this, nor'has" a coupling conductor been provided on the outside'of a cylindiidalibody, but the arrangement has .in a rather" simplifiedform been provided by cutting slots in two concentrical, pipe-formed parts. 7

Although the outer part of course may be the rotor part and the inner part the 'stator part, it is for practical reasons normally more-suita-ble that the outer part is the stator part and the inner part the rotor part. Fig. 4 shows the rotor, in which two slots 21, 22 have been cut, so that between them is formed'a strip-23. This strip is thus in the level of the outer surface of the cylinder'24, but in other respects it functions thesame way as the conductor 17 in Fig. 3. For supporting it one or more disc-formed-elements 25 may be inserted in the interior In a corresponding way, there-have been cut four slots in this part, twofrorn each end. Thus between the slots and 27, a tongue-formedstrip 2.8 is formed, and between'ithe slots: 29 ands!) a second tongue-formed strip.

31 :is formed. The strips 28 and 3.1 correspond to the conductors .15 and 16 in the arrangement according to Fig. 3, and consequently they. are of a length so that they cover the strip 23 by M4 of the mean wave-length within the frequency band to be received. In some cases it may north conductor with the conductor situated on the one side thereof, for instance the east conductor and in a corresponding Way to connect together the output south conductor with one conductor situated at the side thereof, in the actual case thus the west conductor. The instrumentation for reading of direction finding minimum or maximum is connected between the two. conductors thus present. As a' matter of order it should be mentioned that when the question is about ultra short oscil prove that the short circuiting etfectbetween the input:

line conductor and the output one is insufficient. This may, for instance, be due to the fact that one has, in order to make the whole commutator particularly light, made Or it may be due to the outer cylinder havingbeen produced of a material which is not sufficiently well electrically conducting,.but which hasother advantages, for instance low specific weight in combination with high rigidity. ,In such cases the short circuiting effect may be improved by placing betweenthe inner ends of the two tongueformed line conductors 28 and 31 a specific short circuiting ring .of a well conductive material such as copper. Such a ring is shown at 33 in Fig. 5.

A commutator oft-he kind now described can for instance be used as a goniometer. Fig. 6 shows an example of this. Four conductors 34, 35, 36 and 37 are arranged in connection with the stator and lead each to one antenna in .an antenna system foinultra short waves with a directional action, for instance a pair of double dipole antennas, oriented with 90 "displacement of orientation, so that-one distinct dipole antenna will be in each of the four cardinal quarters North (N), West.(W), South (3) and East- (0).- These four conductors thereby correspond to the input line conductors '15 in the arrangement according to Fig.3. Further four output line conductors areprovided, situated intheprolongation of the fou-rinput lineconductors, but-not .visible in the figure. These four.-line*-cond-uctors correspond-to the-line conductor 16 in Fig. 3. For: reading-direction finding maximum: or direction :findingiminimum, respectively, one

caniznow proceed: :in either .of two" different ways.

Firstlyrit is possible/to connect together the output lations, it is of importance that the connecting-conductors are of mutually the same length. This arrangement will allow only two interpretations, but it will introduce a reading error of 45, which has to be taken into consideration at the reading.

Secondly it is possible to combine all the four output conductors with each .otherby means of mutually equally long connection lines. The instrument for reading direction finding minimum or maximum is connected between the connection conductor thus present, on theone side, and thecylindrical casing 32 on the other side: In order not to disturb the symmetry, one should provide a con nection conductor for the cylindrical casing 32 hy con-' meeting the middle points of the free edges oneach of the two broader tongues formedbetween the one-slot of one line conductor and the other slot of the adjacentline conductor, if one is using the arrangement-according to Fig. 5 for creating the line conductors, or one should connect four connection lines of mutually equal length to parts of the cylindrical casing 38, which. are.- symrnetrically situated between the conductors 34,235, 36 and 37,-ifone is using the-arrangement accordingto. Fig. 3, for. bni lding upthe :line. conductors; This arrange. ment'will give no-phase.error, but-it will allow;-of' four interpretations, which;hav.e-.to be taken into considera-. tion at the reading.

Independently of which arrangement is used,, the rotor. is provided with two coupling conductors 319 and 40' of the same kind as the coupling conductor 17 according to Fig. 3 or the coupling conductor 25 according to Fig.4.

When using line conductors or coupling conductors, provided by cutting slots in tube-formed bodies, as shown in connection with Figs. 4 and 5, it is important that the intermediate parts of the cylindrical bodies should have a good short-circuitingeffect. This, amongst others, was the case in the goniometer shown in connection with Fig. 6. In this goniometer it was assumed-that the short circuiting effect Was improved by the .foursections of the cylindrical casing symmetrically being connectedbymu tually equallylong-conductors.

independently of the commutators being-used as :a goniometer or for another purpose, one can achieve .thisefiect by providing specific short circuitingrings in the interior of the casings in question oreventually outside of said casings.

Fig. 7 shows an example of anarrangernent .of.this kind. in the arrangement according to thisQfigure it is assumed that the line conductors 34,735 have been :pro; vided by means of slots in a cylindrical body 36. ,In the central partof said cylindrical body 36, where, there are no slots, at short circuitingring 1,3 7 is provided, and this carries an outer metallic, conductive casingfiS, which is on.its:inside provided with a further number of sym- F metrically provided short circuiting rings. .In the figure only one such short circuiting ring 39'and 40.", respectively, has been shown in each half part of thecylindrical; construction.

The rotor is also made in the way shown in connection with Fig. 4, that means the coupling conductors have been provided by cutting longitudinal slots in a body 41 which is in other respects cylindrically pipe-formed. This body is carried by a shaft '42 by means of a number of hubs provided. symmetrically about-.the ;middle ;,in the form of short circuitingrings 42:, 44, 45, which are,;hovt: ever, z-providejdayith recesses. so'that they will not contactthelcoupling conductors but only the remaining seg:

ments of the cylindrical, metallical conductive casing, existing between the coupling conductors. By this arrangement a very good short circuiting effect is provided.

If in some case one should want a still broader bandwidth of the commutator than the one obtained according to the above, this may be achieved by making the line conductors with a characteristic varying according to their length. Fig. 8 shows an example of this. In the chosen case, the line conductor '46 has been provided by cutting two slots 47 and 48, respectively, in a cylindrical body 49. Thetwo slots however, do not run straight but in obtuse angles, so that they include between themselves a rhombodial figure, open at the sharp corners, said rhombodial figure forming the line conductor 46. Due to the width thus varying this line conductor will have a characteristic varying in the above-mentioned manner. In the middle of the line conductor the strongest current is obtained, and therefore also the line conductor has been given a greater width (less characteristic) in this place. It is obvious, that if one will fully use the advantages of this arrangement, the rhombodial figure should be symmetrical, so that the characteristic is varying in the same way for the input and for the output line conductor.

If one wants to decrease the dimensions of a commutator of the kind now described, it is as a rule not possible due to insulation, technical, and other reasons to cut down the diameter very much. On the other hand, the length of the commutator may be decreased by having the line conductors as well as the coupling conductors running helically along the surface of the cylindrical casing carrying the conductor. Thus, for instance, the two slots 47 and 48 limiting the line conductor are orientated along an axis running as part of a helix on the outer surface of the cylinder 49.

What is claimed is:

1. A high frequency commutator comprising a pair of line conductors, each of said conductors being of a length substantially equal to A of a wave length within the range of frequencies to be transferred, said line conductors being disposed in a straight line relationship and grounded at their free ends, one of said line conductors being an input conductor and the other being an output conductor, means for coupling said input conductor to said output conductor comprising a coupling conductor disposed in parallel arrangement to said line conductors and grounded at both ends, said coupling conductor being of a length substantially equal to /h of a wave length within the range of frequencies to be transferred, and means for varying the distance between said coupling conductor and each of said line conductors.

2. A high frequency commutator according to claim 1 wherein said line conductors are grounded at their free ends to a first metallic cylinder and said coupling conductor is grounded at both ends to a second metallic cylinder, said second cylinder being disposed coaxially within said first cylinder and rotatable in relation thereto.

3. A high frequency commutator according to claim 2 wherein said line conductors are a portion of the metallic surface of said first cylinder and said coupling conductor is a portion of the surface of said second cylinder.

4. A high frequency commutator according to claim 3 wherein a short circuiting ring of a well conductive material is mounted on the surface of said cylinders.

5. A high frequency commutator according to claim 3 wherein said line conductors and said coupling conductor are of varying width.

6. A high frequency commutator according to claim 3 wherein said line conductors and said coupling conductor are angularly disposed with respect to the axis of said cylinders.

References Cited in the file of this patent UNITED STATES PATENTS 

